This paper examines the effects of angle of incidence changes on the optical properties of rugate filters. Like quarterwave dielectric stacks rugate filters are sensitive to tilting: their reflectance bands shift to shorter wavelengths and their optical properties become polarization dependent. Tilting a quarterwave stack also produces a drop in the transmittance in the middle of the passband this drop is called the halfwave hole. In single line rugate filters a similar behavior is observed and multiple holes corresponding to harmonics of the main reflectance bands appear in the pass band. In multiline rugate filters the situation is even more complicated: the large number of harmonics already present is increased by supplementary peaks produced by beating between each family of harmonics. All these reflecting bands are located on the short wavelengths side of the main bands and they can be such that most of the light is reflected. Some possible solutions are suggested involving the use of aperiodic structures. 1.